Collective responses of a large mackerel school depend on the size and speed of a robotic fish but not on tail motion

So far, actuated fish models have been used to study animal interactions in small-scale controlled experiments. This study, conducted in a semi-controlled setting, investigates robot5interactions with a large wild-caught marine fish school (∼3000 individuals) in their natural social environment. Two towed fish robots were used to decouple size, tail motion and speed in a series of sea-cage experiments. Using high-resolution imaging sonar and sonar-video blind scoring, we monitored and classified the school's collective reaction towards the fish robots as attraction or avoidance. We found that two key releasers—the size and the speed of the robotic fish—were responsible for triggering either evasive reactions or following responses. At the same time, we found fish reactions to the tail motion to be insignificant. The fish evaded a fast-moving robot even if it was small. However, mackerels following propensity was greater towards a slow small robot. When moving slowly, the larger robot triggered significantly more avoidance responses than a small robot. Our results suggest that the collective responses of a large school exposed to a robotic fish could be manipulated by tuning two principal releasers—size and speed. These results can help to design experimental methods for in situ observations of wild fish schools or to develop underwater robots for guiding and interacting with free-ranging aggregated aquatic organisms.This work was financed by the Norwegian Research Council (grant 204229/F20) and Estonian Government Target Financing (grant SF0140018s12). JCC was partially supported by a grant from Iceland, Liechtenstein and Norway through the EEA Financial Mechanism, operated by Universidad Complutense de Madrid. We are grateful to A. Totland for his technical help. The animal collection was approved by The Royal Norwegian Ministry of Fisheries, and the experiment was approved by the Norwegian Animal Research Authority. The Institute of Marine Research is permitted to conduct experiments at the Austevoll aquaculture facility by the Norwegian Biological Resource Committee and the Norwegian Animal Research Committee (Forsøksdyrutvalget)

Simple Upper Limb Prosthesis with External Power Support for Cineplastic Control

The work presented in the thesis was motivated by the history of cineplasty and aims to create a supportive system for the body powered upper limb prostheses. A mechanical signal (pulling) from a cineplastic site or a harness system (e.g. shoulder harness) is used to control a prosthetic device. These signals are often too weak to comfortably control the prosthesis leading to fatigue and discomfort. The goal of the thesis was to develop a prosthesis supplying supportive force allowing amputees to use smaller input forces to operate the device. A prototype was realized as a cable-controlled voluntary closing device with an external power support for the force amplification. Easily manufacturable designs and cheap commercial products were preferred while designing the prototype. The mass, pinch force, input cable force, input cable excursion and locking mechanism efficiency were measured using different configurations, and then compared to each other and to commercial products.The support system was able to reduce the necessary input force needed to pinch 15N by 60%, and increase the achieved pinch using a 50N input force by 340%. The system performance was highly dependent on the control gains and the input cable speed. Increased controller gains and decreased input velocity had a similar effect resulting in a higher output force while degrading controllability. After a short training session (30 min) using a prosthesis simulator I was able to use a pair of tweezers to pick and place pieces of wire. The system showed very promising results allowing to decrease the needed force for operating the device; however, the force amplification system has an effect on the feedback quality which should be investigated before making any definitive conclusions. The device can serve as a basis to investigate the effects of control methods on assistive body-powered prostheses